There are several types of field-driven particles in the field of non-emissive displays. One class uses the so-called electrophoretic particle that is based on the principle of movement of charged colloidal particles in an electric field. In an electrophoretic display, the charged particles containing different reflective optical densities can be moved by an electric field to or away from the viewing side of the display, which produces a contrast in the optical density. Another class of field-driven particles are particles carrying an electric dipole. Each pole of the particle is associated with a different optical densities (bi-chromatic). The electric dipole can be aligned by a pair of electrodes in two directions, which orient each of the two polar surfaces to the viewing direction. The different optical densities on the two halves of the particles thus produces a contrast in the optical densities.
To produce a high quality image it is essential to form a plurality of image pixels by varying the electric field on a pixel wise basis. The electric fields can be produced by a plurality pairs of electrodes embodied in the receiver as disclosed in U.S. Pat. No. 3,612,758. A shortcoming is that this solution requires the incorporation of electrodes in the receiver, increasing the receiver complexity.
One difficulty in above described non-emissive display is in displaying color images. The field-driven particles of different colors can be provided in discrete color pixels. This approach requires the colored particles to be placed accurately. Moreover, the electrodes that drive the colored particles also need to in precise registration to the color pixels when different color image planes are formed. This approach is therefore complex and expensive.
The field-driven particles of different colors can also be stacked in layers. But since the field-driven particles are usually opaque and scatter light, the color layers under the top color layer normally receives less input light and reflect less corresponding colored light back to the viewers. The lower color layers therefore have low color reflection densities.
An additional problem in the receivers comprising field-driven particles is forming images which are stable. Typically the images on these receivers must be periodically reformed to keep the image from degrading.